1) Field of the Invention
The invention relates to a redispersible powder composition containing fully hydrolyzed 1-alkylvinyl ester/vinyl ester copolymers and to its use in construction materials, in particular in flowing floor-leveling compounds.
2) Description of the Related Art
Redispersible powders have been used for many years especially in the construction sector as plastic modifiers of hydraulically setting systems. A review of the effect of redispersible powders is given in the journal TIZ (formerly: Tonindustrie-Zeitung) 9, p. 698 (1985). The properties of adhesion, abrasion resistance, scratch resistance and tensile bending strength of hydraulically setting compounds are especially improved by adding redispersible powders. Redispersible powders of this type are described, for example, in EP-A 228,657 or DE-A 2,049,114 and are prepared by spray-drying aqueous polymer dispersions with the addition of polyvinyl alcohol and other additives. The readily flowable powder thus obtained, which has particle sizes between 10 and 250 .mu.m, is redispersed in water to give a dispersion having particle sizes between 0.1 and 5 .mu.m. This dispersion should remain stable over a relatively long period of time, i.e. it should not have a tendency to settle.
An important area of application of redispersible powders is hydraulically setting, flowing floor-leveling compounds. Floor-leveling compounds of this type are known from DE-A 3,028,559 and EP-A 116,524 and in general comprise cement or mixtures of various cements, carefully matched filler combinations, redispersible powders, plasticizing agents, and, if desired, other additives. These compounds are delivered to the construction site in the form of premixed plaster, are combined simply by stirring with water and are applied to the floor. The materials spread to form a smooth surface, which serves either directly as the wear layer or as a base for further coatings. This application always leads to problems. Especially when relatively thick layers are applied, uneven patches, such as craters or pinholes, are formed on the surface. The surface is not as smooth as desired by the customer and has to be reworked.
Accordingly, the object of the present invention was to overcome the disadvantages just described of previously known floor-leveling compounds with respect to the surface condition of coatings manufactured therewith, without losing the advantages produced by the addition of redispersible powders, such as improved abrasion resistance, scratch resistance and adhesion.
Surprisingly, this object could be achieved by adding a fully hydrolyzed 1-alkylvinyl ester/vinyl ester copolymer to the redispersible powder composition.
Polyvinyl alcohols containing alkylvinyl alcohol units of this type have previously only been known as extrudable thermoplastics (JP-A 52/57,256, CA 88:75032n; JP-A 52/60,842, CA 87:118700c), in a mixture with glycerol as melt adhesive composition for bonding paper (JP-A 54/76,634; CA 91:176392x), as cobinder for paper coating compositions (DE-A 3,622,820), as rheological additives for aqueous dispersions (DE-A 3,724,331) and as sizing agents for yarns (DE-A 3,724,332).